Proton pump inhibitors (PPI) are potent inhibitors of gastric acid secretion by inhibiting H+,K+-ATPase, the enzyme involved in the final step of hydrogen ion production in the parietal cells, and highly effective in the treatment of gastric acid related diseases such as gastric ulcer, bleeding ulcer, duodenal ulcer, NSAID-induced ulcer, peptic ulcer, erosive esophagitis, gastroesophageal reflux disease, Helicobacter pylori infections, Zollinger-Ellison syndrome, NSAID or COX2 inhibitor-associated prophylaxis, Dyspepsia and gastritis in humans. There are currently five different PPIs available including omeprazole, lansoprazole, rabeprazole, esomeprazole and pantoprazole. These agents are all substituted benzimidazoles that inhibit final common pathway of gastric acid secretion.
Gastroesophageal reflux refers to the retrograde movement of gastric contents from the stomach into the esophagus. When this reflux leads to symptomatic conditions or histologic alterations, it is known as gastroesophageal reflux disease (GERD). The reflux of the gastric material into the esophagus may lead to inflammation, hyperplasia of the esophageal lining, esophageal ulcers and Barrett's esophagus. GERD is usually a chronic, relapsing condition. Approximately 44% of the adult US population experiences heartburn at least monthly, 18% experience heartburn at least twice weekly, and 7% experience heartburn daily. Approximately one million Americans have erosive esophagitis, and as many as 20% of these individuals develop complications like esophageal strictures. Therapy for GERD is directed at eliminating the patient's symptoms, decreasing the frequency and duration of reflux, healing the injured mucosa and preventing the development of complications. The management of GERD includes lifestyle modification, acid suppression therapy, and possibly surgery. Lifestyle modifications include elevation of, the head of the bed, dietary changes, smoking cessation and weight loss. Proton pump inhibitors are the mainstay of acid suppression therapy for GERD.
Peptic ulcer disease is also a chronic disease typified by exacerbations and remissions. About 10% of all Americans will develop a peptic ulcer during their lifetime. Duodenal ulcer is more common than gastric ulcer. Duodenal ulcer usually occurs in individuals between 25 and 55 years old whereas gastric ulcer most often occurs in individuals between 55 and 65 years old. Peptic ulcers develop from abnormalities in acid secretion, mucosal defense and motility. Helicobacter pylori and nonsteroidal antiinflammatory medications also play an important role in the development of ulcer disease. Drug therapy for peptic ulcer disease is aimed at reducing gastric acidity and enhancing mucosal defense.
Zollinger-Ellison syndrome (ZES) is an acid hypersecretory state caused by a gastrin secreting tumor in the pancreas. ZES occurs in about 0.1% of patients with duodenal ulcer. It is diagnosed when patients have a basal acid output greater than 15 meq/hr. Proton pump inhibitors are the drugs of choice for the management of ZES.
The proton pump inhibitors are the most effective acid suppression drugs available. All five of the available agents appear to be equally efficacious for treating GERD, gastric ulcer and duodenal ulcer. However it is reported that esomeprazole 40 mg was more effective in controlling acid secretion than omeprazole 40 mg, pantoprazole 40 mg or lansoprazole 30 ng (Medical Letter vol. 43 (W1103B), 2001). Because pantoprazole and rabeprazole tablets cannot be crushed or made into a suspension formulation, these two PPIs are not well-suited to pediatric patients or patients with swallowing difficulties (CIGNA HEALTHCARE COVERAGE POSITION Number 4005).
Prostaglandins (hereinafter, referred to as PGs) are members of class of organic carboxylic acids, which are contained in tissues or organs of human or other mammals, and exhibit a wide range of physiological activity. PGs found in nature (primary PGs) generally have a prostanoic acid skeleton as shown in the formula (A):

PGs are classified into several types according to the structure and substituents on the five-membered ring, for example,
Prostaglandins of the A series (PGAs);
Prostaglandins of the B series (PGBs);
Prostaglandins of the C series (PGCs);
Prostaglandins of the D series (PGDs);
Prostaglandins of the E series (PGEs);
Prostaglandins of the F series (PGFs);
and the like. Further, they are classified into PG1s containing a 13,14-double bond; PG2s containing, 5,6- and 13,14-double bonds; and PG3s containing 5,6-, 13,14- and 17,18-double bonds. PGs are known to have various pharmacological and physiological activities, for example, vasodilatation, inducing of inflammation, platelet aggregation, stimulating uterine muscle, stimulating intestinal muscular activity, anti-ulcer effects and the like. The major prostaglandins produced in the human gastrointestinal (GI) system are those of the E, I and F series (Sellin, Gastrointestinal and Liver Disease: Pathophysiology, Diagnosis, and Management. (WB Saunders Company, 1998); Robert, Physiology of the Gastrointestinal Tract 1407-1434 (Raven, 1981); Rampton, Prostaglandins: Biology and Chemistry of Prostaglandins and Related Eicosanoids 323-344 (Churchill Livingstone, 1988); Hawkey, et al., Gastroenterology, 89: 1162-1188 (1985); Eberhart, et al., Gastroenterology, 109: 285-301 (1995), the cited references are herein incorporated by reference).
Under normal physiological conditions, endogenously produced prostaglandins play a major role in maintaining GI function, including regulation of intestinal motility and transit, and regulation of fecal consistency. (Sellin, Gastrointestinal and Liver Disease: Pathophysiology, Diagnosis, and Management. (WB Saunders Company, 1998); Robert, Physiology of the Gastrointestinal Tract 1407-1434 (Raven, 1981); Rampton, Prostaglandins: Biology and Chemistry of Prostaglandins and Related Eicosanoids 323-344 (Churchill Livingstone, 1-988), Hawkey, et al., Gastroenterology, 89: 1162-1188 (1985); Eberhart, et al., Gastroenterology, 109: 285-301 (1995); Robert, Adv Prostaglandin Thromboxane Res, 2:507-520 (1976); Main, et al., Postgrad Med J, 64 Suppl 1: 3-6 (1988); Sanders, Am J Physiol, 247: G117 (1984); Pairet, et al., Am J Physiol., 250 (3 pt 1): G302-G308 (1986); Gaginella, Textbook of Secretory Diarrhea 15-30 (Raven Press, 1990)). When administered in pharmacological doses, both PGE2 and PGF2α have been shown to stimulate intestinal transit and to cause diarrhea (Robert, Physiology of the Gastrointestinal Tract 1407-1434 (Raven, 1981); Rampton, Prostaglandins: Biology and Chemistry of Prostaglandins and Related Eicosanoids 323-344 (Churchill Livingstone, 1988); Robert, Adv Prostaglandin Thromboxane Res, 2:507-520 (1976)). Furthermore, the most commonly reported side effect of misoprostol, a PGE1 analogue developed for the treatment of peptic ulcer-disease, is diarrhea (Monk, et al., Drugs 33 (1): 1-30 (1997)) The references cited in this paragraph are herein incorporated by reference.
PGE or PGF can stimulate intestinal contraction, but the enteropooling effect is poor. Accordingly, it is impractical to use PGEs or PGFs as cathartics because of side effects such intestinal contraction that cause abdominal pain.
Multiple mechanisms, including modifying enteric nerve responses, altering smooth muscle contraction, stimulating mucous secretion, stimulating cellular ionic secretion (in particular electrogenic Cl− transport) and increasing intestinal fluid volume have been reported to contribute to the GI effects of prostaglandins (Robert, Physiology of the Gastrointestinal Tract 1407-1434 (Raven, 1981); Rampton, Prostaglandins: Biology and Chemistry of Prostaglandins and Related Eicosanoids 323-344 (Churchill Livingstone, 1988); Hawkey, et al., Gastroenterology, 89: 1162-1188 (1985); Eberhart, et al., Gastroenterology, 109: 285-301 (1995); Robert, Adv Prostaglandin Thromboxane Res, 2:507-520 (1976); Main, et al., Postgrad Med J, 64 Suppl 1: 3-6 (1988); Sanders, Am J Physiol, 247: G117 (1984); Pairet, et al., Am J Physiol, 250 (3 pt 1): G302-G308 (1986); Gaginella, Textbook of Secretory Diarrhea 15-30 (Raven Press, 1990); Federal Register Vol. 50, No. 10 (GPO, 1985); Pierce, et al., Gastroenterology 60 (1): 22-32 (1971); Beubler, et al., Gastroenterology, 90: 1972 (1986); Clarke, et al., Am J Physiol 259: G62 (1990); Hunt, et al., J Vet Pharmacol Ther, 8 (2): 165-173 (1985); Dajani, et al., Eur J Pharmacol, 34(1): 105-113 (1975); Sellin, Gastrointestinal and Liver Disease: Pathophysiology, Diagnosis, and Management 1451-1471 (WB Saunders Company, 1998)). Prostaglandins have additionally been shown to have cytoprotective effects (Sellin, Gastrointestinal and Liver Disease Pathophysiology, Diagnosis, and Management. (WB Saunders Company, 1998); Robert, Physiology of the Gastrointestinal Tract 1407-1434 (Raven, 1981); Robert, Adv Prostaglandin Thromboxane Res 2:507-520 (1976); Wallace, et al., Aiiment Pharmacol Ther 9: 227-235 (1995)). The references cited in this paragraph are herein incorporated by reference.
U.S. Pat. Nos. 5,225,439, 5,166,174, 5,284,858, 5,428,062, 5,380,709, 5,886,034 and 6,265,440 (the cited patents are herein incorporated by reference) describe that certain prostaglandin E compounds are effective for the treatment of ulcers such as duodenal ulcer and gastric ulcer.
U.S. Pat. No. 5,317,032 to Ueno et al describes prostaglandin analog cathartics, including the existence of bicyclic tautomers and U.S. Pat. No. 6,414,016 to Ueno describes the bicyclic tautomers as having pronounced activity as anti-constipation agents (the cited patents are herein incorporated by reference). The bicyclic tautomers, substituted by one or more halogen atoms can be employed in small doses for relieving constipation. At the C-16 position, especially, fluorine atoms, can be employed in small doses for relieving constipation.
U.S. Patent publication No. 2003/0130352 to Ueno et al (the cited publication is herein incorporated by reference) describes prostaglandin compound opens and activates chloride channels, especially ClC channels, more especially ClC-2 channel.
U.S Patent publication No. 2003/0166632 to Ueno (the cited publication is herein incorporated by reference) described ClC-2 channel opener is effective for the treatment of a disease or a condition responsive to opening of ClC-2 channel.
U.S. Patent publication No. 2003/0119898 to Ueno et al (the cited publication is herein incorporated by reference) describes specific composition of a halogenated prostaglandin analog for the treatment and prevention of constipation.
U.S. Patent publication No. 2004/0138308 to Ueno et al (the cited publication is herein incorporated by reference) describes chloride channel opener, especially a prostaglandin compound for the treatment of abdominal discomfort, and the treatment of functional gastrointestinal disorders such as irritable bowel syndrome and functional dyspepsia.
International Publication No. WO00/35448 (the cited publication is herein incorporated by reference) describes a pharmaceutical formulation comprising a proton pump inhibitor and specific gastric antisecretory prostaglandin analogue for use in the treatment of gastrointestinal disorders.
It is reported that misoprostol, one of the gastric antisecretory prostaglandin analogue inhibits platelet aggregation (Journal of Physiology and Pharmacology 2002, 53, 4, 635-641). It is also reported that ornoprostil, one of the gastric antisecretory prostaglandin analogue, has an anti-platelet agglutination effect to enhance the bleeding, so it should be carefully administered to the patient with hemorrhagic ulcer (ornoprostil package insert). The cited references are herein incorporated by reference.